The invention relates to a telescopic bar for opening a movable cover, notably on an aircraft engine nacelle.
Aircraft engines are enclosed in nacelles, some parts of which are movable covers which can open so that access can be gained to the engine. Conventionally, these covers have cross sections in the shape of an arc of a circle, are hinged on a mast fixed to the wing by their top edge and are provided with locking means at their bottom edge so as to hold them normally closed. The opening method consists first of all of undoing the locking means and then raising the covers by hand if their weight so permits or using jacks provided for this purpose. When opening is complete, bars are installed between the cover and the now exposed engine in order to prevent the covers from falling. These bars must be telescopic, formed by sections sliding in each other and which are locked in the deployed position by controlling locking systems: they are in fact kept beforehand in the adjoining space between the cover and the engine, which is too cramped for them to be able to be left in the deployed state. In the design known up to the present time, the bars are hinged at one end on the cover, approximately half way up it, and the other end terminates in a clamp which closes on a handle on the cover when the bars are stored.
Once the cover is unlocked and raised, an operator must therefore detach the clamp on the bar from the cover handle, and then pull the bar so that its sections are deployed, mutually lock the sections when their deployment is complete and engage the clamp in a handle fixed to the engine in order to install the bar and guarantee opening of the cover. These operations are relatively slow and the operator can obviously do nothing else during this time: if the cover does not have motorised opening (which is generally the choice with lightweight covers so as not to complicate their design), it is therefore necessary to have the cover raised by at least one other operator whilst the first one takes care of the bar. The same applies when the cover is to be closed again. Using several operators for such simple operations is to be regretted.
The object of the invention is therefore to accomplish all the operations of opening a movable cover on an aircraft engine nacelle by means of a single operator by virtue of a novel design of the telescopic bar intended to hold the cover open under maximum safety conditions, including in the case of high wind (regulations of the DGAC, FAA, etc).
In its most general form, the invention thus relates to a telescopic bar for opening a movable cover on an aircraft engine nacelle, the movable cover having an edge hinged on a mast or another  fixed  part of the engine or nacelle, and a bottom edge equipped with means of locking on the nacelle or on another movable cover on the nacelle, the bar being composed of sections comprising mutually sliding first and second sections provided with locking systems able to be brought into service for an extension position of the bar in which the movable cover is held open and a single unlocking mechanism overriding the service of the locking system, characterised in that it is permanently hinged on the engine and on the bottom edge of the movable cover at opposite ends, and in that the unlocking mechanism has a handle situated close to the end articulated on the bottom edge of the movable cover.
It can be seen that the bar, permanently hinged on the cover at one end and on the engine at the other, requires no manipulation during the opening of the cover. The connection of the bar to the opening edge of the cover enables the operator lifting the cover by this opening edge to reach the bar without difficulty in order to lock it, at least if locking is manual, or to unlock it when the cover is to be closed again. A particular design of the bar in two sections of unequal length can make it possible to hinge it at the points indicated, as will be seen subsequently, whatever the shape or kinematics of opening of the cover.
The advantages of the invention cannot be achieved by systems of bars where the unlocking mechanisms are distant from the point of hinging of the bar on the cover, nor by those where the point of articulation of the bar on the cover is distant from the bottom edge of the latter. A remarkable element of the invention is that the unlocking mechanism is separate from the locking system, which is situated at the junction of the sections of the bars.
In concrete terms, it is advantageous for the section to be articulated on the opening edge of the movable cover, the first section to be hinged on the engine and to slide in the second section, and for the unlocking mechanism to comprise a tube sliding on the second section and fixed to a control handle.
A particularly advantageous locking and unlocking mechanism is obtained if the handle is situated immediately behind the movable cover, the sliding tube comprises an internal receptacle opposite the handle, the section has at a minimum one drilling passing through it at an end opposite the opening edge of the movable cover, the first section has in it an external groove at an end opposite the engine, the locking mechanism also comprises a spring disposed between the second section and the tube and moving the handle away from the cover, and balls are disposed in the drillings whilst projecting out into the receptacle or into the groove. The hinged edge and the opening edge correspond respectively to a top edge and a bottom edge in the underwing nacelle whose description follows, but the joint between the covers can be different, for example with a fuselage carrying engines (MD 90 or other, where this joint is horizontal). The invention would apply under the same conditions.